This invention relates to photographic materials. In a preferred form it relates to base materials for photographic reflection and transmission display.
It is known in the art that photographic display materials are utilized for advertising, as well as decorative displays of photographic images. Since these display materials are used in advertising, the image quality of the display material is critical in expressing the quality message of the product or service being advertised. Further, a photographic display image needs to be high impact, as it attempts to draw consumer attention to the display material and the desired message being conveyed. Typical applications for display material include product and service advertising in public places such as airports, buses and sports stadiums, movie posters, and fine art photography. The desired attributes of a quality, high impact photographic display material are a slight blue density minimum, durability, sharpness, and flatness. Cost is also important, as display materials tend to be expensive compared with alternative display material technology such as lithographic images on paper. For display materials, traditional color paper is undesirable, as it suffers from a lack of durability for the handling, photo processing, and display of large format images.
Prior art photographic display materials historically have been classified as either reflection or transmission. Reflection display material typically is highly pigmented image supports with a light sensitive silver halide coating applied. Reflection display materials are typically used in commercial applications where an image is used to convey an idea or message. An application example of a reflection display material is product advertisement in a public area. Prior art reflection display materials have been optimized to provide a pleasing image using reflective light. Transmission display materials are used in commercial imaging applications and are typically backlit with a light source. Transmission display materials are typically a clear support with a light sensitive silver halide and an incorporated diffuser (to hide the xe2x80x9cshow throughxe2x80x9d of the lamps used to provide viewing illumination) or a substantially transparent support coated with a light sensitive silver halide emulsion which requires a diffusing screen to be placed behind the material as a means to obscure the xe2x80x9cshow throughxe2x80x9d of the lamps used to provide illumination to the media. Prior art transmission display materials have been optimized to provide a pleasing image when the image is backlit with a variety of light sources. Because prior art reflection and transmission products have been optimized to be either a reflection display image or a transmission display image, two separate product designs must exist in manufacturing, and two inventories of display materials must be maintained at the photofinishing printing site. Further, when the quality of the backlighting for transmission display material is diminished when, for example, a backlight burns out or the output of the backlight decreases with the age, the transmission image will appear dark and reduce the commercial value of the image. It would be desirable if an image support could function both as a reflection and transmission display material.
Prior art transmission display materials use a high coverage of light sensitive silver halide emulsion to increase the density of the image compared to photographic reflection print materials. While increasing the coverage does increase the density of the image in transmission space, the time to image development is also increased as the coverage increases. Typically, a high-density transmission display material has a developer time of at least 110 seconds compared to a developer time of 45 seconds or less for photographic print materials. Prior art high-density transmission display materials, when processed, reduce the productivity of the development lab. Further, coating a high coverage of emulsion requires additional drying of the emulsion in manufacturing, which reduces the productivity of emulsion coating machines. It would be desirable if a transmission display material was high in density and had a developer time less than 50 seconds.
Prior art reflection photographic materials with a polyester base use a TiO2 pigmented polyester base onto which light sensitive silver halide emulsions are coated. It has been proposed in WO 94/04961 to use opaque polyester containing 10% to 25% TiO2 for a photographic support. The TiO2 in the polyester gives the reflection display materials an undesirable opalescent appearance. The TiO2 pigmented polyester also is expensive because the TiO2 must be dispersed into the entire thickness, typically from 100 to 180 xcexcm. The TiO2 used in this fashion also gives the polyester support a slight yellow tint, which is undesirable for a photographic display material. For use as a photographic display material, the polyester support containing TiO2 must be tinted blue to offset the yellow tint of the polyester, causing a loss in desirable whiteness and adding cost to the display material.
Prior art photographic display material uses polyester as a base for the support. Typically the polyester support is from 150 to 250 xcexcm thick to provide the required stiffness. Prior art photographic display materials are typically coated with light sensitive silver halide imaging layers on one side of the support. Exposure devices have been built to expose only one side of prior art display materials, thus there is little concern for print platen design. For example, exposure devices that use a vacuum roll for holding the media during exposing typically employ slots for vacuum. These slots act as xe2x80x9cblack trapsxe2x80x9d (areas where exposing energy will be lost and have little secondary reflection) which in a duplitized emulsion system will result in uneven density for the backside image.
In U.S. Pat. No. 6,030,756 duplitized silver halide imaging layers are discussed for use as a display material. In U.S. Pat. No. 6,030,756, both the top and bottom images are exposed by exposing the topside silver halide imaging layers. While the display material in U.S. Pat. No. 6,030,756 does form an excellent image capable of an exceptional reflection and transmission image, the display material in U.S. Pat. No. 6,030,756 does suffer from uneven backside image density when placed against a non-uniform reflecting platen and subsequently exposed with light energy.
It has been found that the prior art structure disclosed in U.S Pat. Nos. 6,030,756 and 6,017,685 is plagued with uneven density variations as a result of uncontrolled backscatter in certain printers in the absence of an antihalation layer. As is obvious, this undesirable exposure can be effectively controlled by the addition of an antihalation layer. However, the presence of an antihalation layer was found to give greatly diminished imaging efficiency, particularly in the backside imaging layer. In this case, the curve shape of an exposure versus density plot reveals a significant break at the mid-scale that leads to significantly lower shoulder and maximum density, as compared to an element without the antihalation layer. Although in principle it may be possible to recover this density with the addition of silver and coupler to the backside imaging layers, this would be very undesirable on a material cost basis and also due to the desire to keep the required photo processing time to a minimum.
There is a continuing need for an improved product that will present a bright reflective image when viewed directly and also provide a sharp bright image of sufficient dye density when back illuminated.
It is an object of the invention to overcome disadvantages of display materials.
It is another object to provide a superior, lower cost, and stronger display material.
It is another object to provide a backside image of sufficient dye density when the only exposing light is on the front side of the display element.
These and other objects of the invention are accomplished by a display material comprising a base, said base comprising a polyester sheet comprising at least one voided polyester diffusion layer, at least one topside photosensitive silver halide layer on the topside of said base and at least one bottom side photosensitive layer on the bottom side of said base, below said at least one bottom side emulsion layer a tone enhancing layer, and below said tone enhancing layer an antihalation layer, wherein said display material has a light transmission of between 35 and 60 percent in the developed Dmin areas of the display material.
The invention provides a material that will, when imaged and developed, result in a bright sharp reflective image when viewed in ambient front surface lighting conditions, as well as allowing for a pleasing image of sufficient dye density when illuminated with a transmission light source. In a preferred form the invention provides a product that may be provided with a silver halide image on each side but still retain a single exposure step and short processing time.